Without limiting the scope of the invention, its background will be described in relation to a system and method for printing on lenticular sheets, as an example.
The use of lenticular sheets to transmit images to appear to an observer as three-dimensional, and to appear different from different viewer positions, to give a perception of changing as the observer moves, is known. A summary of certain typical features, and some general examples, are given for convenience.
Lenticular sheets, as they are generally known, include a plurality of semi-cylindrical lenses, or lenticules, arranged side-by-side, in a plane, each extending in the same direction. The lenticular sheets are typically formed of a substantially transparent plastic and are overlaid onto an ink-supporting substrate or medium on which a plurality of specially formatted images are disposed.
Lenticular sheets, though, permits display of an image on a hard copy surface to appear three-dimensional. One method for this displaying is to take a picture of a scene from a first location, and then move the camera a lateral distance to a second location and take a picture of the same scene. The picture taken from the first position may be called the left image and the picture taken from the second position may be called the right image. There is a parallax between the two images, due to the lateral displacement between the respective positions from which the left and right pictures were taken. The parallax is exploited by rasterizing the left and right images or pictures into, for example, sixty-four vertical strips each. The rasterizing can be done by converting the pictures into a digital pixel array and then dividing the array into sixty-four strips, typically in a vertical direction. The left and right images are disposed on a medium, typically by placing the first vertical stripe of the left image next to the first vertical stripe of the right image, and then the second vertical stripe of the left image next to the second vertical stripe of the right image. The arrangement is typically repeated so that, for example, the sixty-four vertical stripes of the left image are interspersed with sixty-four vertical stripes of the right image, in an alternating pattern.
To increase the number of viewing positions from which the observer will see a three-dimensional image, a greater number of rasterized images are created, and a correspondingly greater number of raster lines are disposed under each lenticule. For example, instead of a left eye and right eye picture taken from a single head-on view, a plurality of left/right pictures can be taken, each from a different view. Picking three views as an example, the above-described head-on view is generated as described, and then a first flank view is generated by taking a left eye picture and a right eye picture, from a position to the left and right, respectively, of a second view position. The second view position may be displaced, for example, 10 degrees left from the head-on position. Next a right flank view is generated by taking a left picture and a right picture, from a position to the left and right, respectively, of a third view position. The third view position is displaced, for this example, 10 degrees to the right of the head-on position.
Inkjet printers have been identified as a preferred apparatus for printing lines of pixels, or raster lines, for viewing through lenticular sheets. However, inkjet printers have inherent limitations as to the minimum dot size they can print, and limitations on the minimum spacing from one dot to the next. The prior art selects line widths and spacing based on trial-and-error, or to match standard or vendor-supplied lenticular sheets. Prior art lenticular sheets, however, are manufactured without particular consideration to the specific printing capabilities of the printer, or of the type of printer, that will be used to print the interleaved pixel lines, i.e., raster lines, on the medium. The spacing between the lenticules or microlenses, though, is one of the ultimate factors bearing on the width of the pixel lines, and the number and spacing of pixel lines. More particularly, if the number of pixel lines is selected which results in a line, or pixel width, or pixel-to-pixel spacing smaller than the ink-jet printer can produce the image quality will be substantially degraded. On the other hand, if the number of pixel lines is selected based on an overly conservative estimate of the printer's capabilities, the final product will have an image quality that is lower than what could have been obtained.
A further problem has been identified with using inkjet printers to print on a lenticular sheets. The problem is that, due to human error, shortcomings in the printer feed mechanism, and other causes, the orientation of the lenticular sheets when the printing operation is performed may not be correct. As a result, as the lenticular sheets progresses through the printer there will be a migration in the position of the first lenticule in the direction of the printer carriage.
Still another problem identified is that regardless of the nominal spacing between lenticules, the raster image processing associated with an inkjet printer cannot space the pixels as correctly as attainable absent use of measured data representing the lenticule spacing of the lenticule sheets that is actually being printed on.